A fluid end refers to that part of a pump apparatus which actually moves fluid from a pump inlet to a pump discharge. In a piston type pump, this would comprise the cylinder or liner, the piston, and the valves. This invention is directed toward a different type of fluid end for use primarily in the oil well drilling industry, and more specifically, to a fluid end for pumping mud from a mud supply into a drill string.
During the last twenty years or so, most of the oil well drilling pumps, called mud pumps, have been of the single acting piston type. The fluid end is usually arranged as shown on pages 2 and 3 of the IADC Drilling Manual, FIGS. J1 through J6. While placement of the valves may vary from one pump to another, the overall arrangement and fluid flow is about the same. The valves are designed such that the flow of fluid is in one direction only, that is, as the piston is moved to increase the volume in the variable chamber of the fluid end, the suction valve opens, allowing fluid to fill that volume. As the piston moves in the other direction, the suction valve closes, and the discharge valve opens, moving the fluid from the variable chamber into the discharge line. This design, while it works, has several serious drawbacks; primarily in the fluid end body itself. The fluid end body provides a fluid passage that extends from the suction valve, to the liner piston, to the discharge valve, and this passage must be large enough not only for the fluid passage but also for installation and removal of the valves, and with some designs, also the liner. The intersection of the various bores as well as the physical size thereof form a high stress area at the juncture of these bores. Fatigue cracks occur at these stress risers, resulting in early fatigue failure of the fluid end.
Another problem that can occur in the body of many prior art fluid ends is the installation of the valve seat into the body. If these parts are not properly installed, or if the seat or body has any flaw or debris that would keep the seat from fitting the body properly, the fluid will eventually erode or cut a passage from the high pressure side, about the valve seat, and to the lower pressure side, resulting in excessive erosion and the requirement of early replacement of the valve or the fluid end body.
It is believed that this invention eliminates the first problem, and, while it may not completely eliminate the erosion problem, it should significantly reduce the replacement cost thereof.
In approaching the first problem, it was recognized that the intersecting bores must be eliminated. This is accomplished by the present invention by placing one of the valves in the pump piston itself and using a horizontal type valve rather than the usual vertical valve. When the valve is relocated into the piston, then the piston rod must pass through a seal. This rod seal is placed on the low pressure or suction side of the piston or working chamber. The problem with this unique design is its horizontal orientation. A prior art type valve used in this new design would exhibit accelerated wear by the fluid being pumped, and this would prevent the valve from seating properly, and therefore bring about early valve failure. This problem is solved by the provision of a unique ball valve assembly. The ball valve rolls in a cage, rather than sliding in a guide and therefore cannot get cocked as with the present known valve arrangement. Further, to prevent the weight of the ball from becoming a problem due to the inertia of the reciprocating piston, particularly in the larger sizes and in the piston installed valve, a hollow ball is proposed. In most cases, the ball weight will be adjusted to less than four pounds per gallon of displaced fluid, and may therefore be made to actually float in eighteen pound per gallon mud, for example.